Rolling Wave Planning
As discussed in Best Practice 1, a comprehensive IMS should reflect all the activities of a program and should recognize that uncertainties and unknown factors in schedule estimates can stem from, among other things, limited data. A schedule incorporates different levels of detail depending on the information available at any point in time. Near-term effort will be planned in greater detail than long-term effort.
Detailed activities within a low-level schedule represent tasks that are typically 4 to 8 weeks long.15 They reflect near-term, well-defined effort, typically within 6 months to a year of the current date. But it is often difficult to forecast detailed work clearly beyond 9 to 12 months. In general, the length of the near-term detail planning period should be decided by program management. It depends on the project’s size, phase, scope, risk, and complexity. For example, some schedules may be planned in detail for only 2 or 3 months.
Effort beyond the near term that is less well defined is represented within the schedule as planning packages. Planning packages summarizing work in the distant future can be used as long as they are defined and estimated as well as possible. Planning packages are planned at higher levels such that a single activity may represent several months of effort, generic work to be accomplished by a trade or resource group, or even a future contract or phase.
As time passes and future elements of the program become better defined, planning packages are broken into detailed work packages. This incremental conversion of work from planning packages to work packages is commonly known as “rolling wave” planning. Rolling wave planning continues for the life of the program until all work has been planned in detail.16 A best practice is to plan the rolling wave to a design review, test, or other major milestone rather than to an arbitrary period such as 6 months.
Moreover, detail should be included in the schedule whenever possible. That is, if portions of far-term effort are well defined, they should be included in the IMS as soon as possible. However, care should be taken not to detail ill-defined far-term effort so soon as to require constant revision as time progresses. More detail does not necessarily mean greater accuracy, and pursuing too much detail too early may be detrimental to the schedule’s quality.
While planning packages represent far-term effort that has not yet been planned in detail, each planning package must still be traceable to WBS elements within the IMS. Moreover, planning packages should be logically linked within the schedule to create a complete picture of the program from start to finish and to allow the monitoring of a program’s critical path. Planning packages that are on or near the critical path or that carry significant risk should be broken into smaller activities to better understand workflow. As durations and resource assignments are refined over time, so too is the detailed sequence of activities.
Appendix III provides more information on work packages, rolling wave planning, and earned value management.
Durations of detail activities are discussed in Best Practice 4.↩︎
Rolling wave planning with portions of effort that align to significant program increments, blocks, or updates is sometimes referred to as “block planning.” The distinction is that rolling wave planning is performed with a certain periodicity while block planning is performed to specific stages in the project. In either case, details are added to the schedule incrementally as the project progresses.↩︎